A Study to Evaluate the Efficacy and Safety of ASP1707 in Postmenopausal Female Patients With Rheumatoid Arthritis Taking Methotrexate

Inclusion Criteria: * Subject has RA that was diagnosed according to the 1987 ACR criteria or the 2010 ACR/EULAR criteria. * Subject meets the ACR 1991 Revised Criteria for the Classification of Global Functional Status in RA Class I, II or, III. * subject has active RA as evidenced by both of the followings: * ≥ 6 tender/painful joints (using 68-joint assessment) * ≥ 6 swollen joints (using 66-joint assessment) * CRP (C-reactive protein) of \> 0.3 mg/dL or ESR (Erythrocyte sedimentation rate) of \> 28 mm/hr at screening. * Subject who continuously received MTX and who is able to continue stable dose of MTX. * Subject who did not receive the following drugs, or received the drugs with stable dosage: Non-steroidal anti-inflammatory drugs, oral morphine or equivalent opioid analgesics, acetaminophen, or oral corticosteroids. Exclusion Criteria: * Inadequate responders to a biologic DMARD (Disease-modifying antirheumatic drug). * Subject has taken other investigational research products are prohibited within 12 weeks (84 days) or within 5 half-lives, whichever is longer, prior to screening. * Subject has undergone surgery which has residual effects on the assessed joints, or is scheduled to undergo surgery that may affect the study evaluation of the assessed joints. * Subject has another type of inflammatory arthritis other than RA. * Subject who meets any of the following criteria of laboratory values at screening: * White blood cell count \<4000/μL * Platelet count \<100000/μL * ALT (Alanine Aminotransferase) ≥ 2 x ULN (Upper Limit of Normal) * AST (Aspartate Aminotransferase) ≥ 2 x ULN * Total bilirubin ≥ 1.5 x ULN * Positive Hepatitis B surface antigen, Hepatitis B virus-DNA quantitation, or Hepatitis C virus antibody * Subject has a positive QuantiFERON-TB Gold test or T-spot. * Subject has a history of or concurrent malignant tumor. * Subject has any ongoing severe, progressive, or uncontrolled renal, hepatic, hematological, gastrointestinal, metabolic, endocrine, pulmonary, cardiac, neurological, infectious, or autoimmune disease except for RA, or diseases which preclude the subject's participation in the study. * Subject has a history of clinically significant allergy. * Subject has clinically significant abnormalities on the 12-lead Electrocardiogram. * Subject has a history of positive Human Immunodeficiency Virus infection.